The German, who competed in the 1500 metres freestyle event at Rio 2016, clocked a time of  1 hour 55min 40.02sec for the 10 kilometres race in Hungary and was followed by Olympic champion and Doha World Series winner Ferry Weertman of the Netherlands. 

Weertman, who had finished fourth in Setubal in Portugal last week, finished nearly 17 seconds behind. 

France's Axel Reymond closed the podium four seconds later in 1:55:59.1.

“The waves were a bit new experience for me as I didn’t get used to them as a pool swimmer”Wellbrock said. 

"We had flat waters in Gravelines so this was hard and I wanted to reserve as much energy as possible over the first five kilometres, then speeded up in the second part and gave everything after the last buoy. 

"I’m happy that this worked."

Brazil's Ana Marcela Cunha, a three-time world 25km champion, won the women's event in 2:05:53.1 by just three-hundredths of a second.

Setubal winner Haley Anderson bagged the silver medal today in 2:05:53.4, while 2016 overall Series winner Rachele Bruni of Italy stole the bronze in 2:05:54.7.

 It was Cunha's second victory here, having also won in 2015.

Cunha had finished seventh in Setubal last weekend and took the silver medal in the Seychelles last month.

"It was all good our there," she said. 

"I love Balaton, I always achieve great results here just like today. 

"It was a great finish, now I could do everything according to my plans and finally won a race this year."

The next stop on in the Marathon Swim World Series is due to be in St Jean in Canada on July.

It will be the fifth of nine events.